The invention relates to a pocket for the positive electrodes of lead accumulators or batteries, consisting of two pieces of a textile sheet material, which are held together by parallel seams dividing the pocket into parallelly disposed tubelets.
The positive plates of lead accumulators are today commonly formed of a plurality of bars disposed adjacent one another. These are surrounded by tubelets of a textile material of such a nature that the required active composition can be filled into the intervals between the bar and the individual tubelet.
Since the active composition changes its volume with the state of charge of the accumulator, the mechanical strength of the tubelets must be very great.
It is known to use such tubelets drawn on individually or in the form of tubelet pockets. The latter have the advantage of easier manufacture and assembly.
German Utility Model No. 74 25 570 describes a tubelet pocket which is made of a nonwoven fabric. Such pockets have the advantage that the individual fibers are in random arrangement and thus form a kind of labyrinth which is outstandingly effective as a filter for solid particles of the active composition, but which on the other hand offers no appreciable resistance to the passage of ions. The use of tubelet pockets of nonwoven fabric consequently results in a very low internal resistance in the battery, which is desirable. Such nonwoven pockets are relatively elastic, i.e., they adapt themselves to a great extent to the volume of the active composition as it continuously varies in operation. For example, nonwoven tubelets withstand the pressure occurring under extreme brief stresses when tubelets of necessarily less elastic woven fabrics burst. The elasticity of the nonwoven tubelet pocket also enables the confined active composition to remain always relatively loose, and this provides for a good capacity in the cells by allowing the particles to present a large surface area in a desirable manner. However, it can be considered a disadvantage of such pockets that the known nonwoven tubelets, under certain circumstances, are not capable of withstanding in the long run the mechanical stress produced by the constant swelling and shrinking of the active composition in the tubelets in the charging and discharging processes.
A loosening of the bond between the fibers ultimately leads to a high permanent expansion, with the danger of premature failure of the cell due to sedimentation.
On account of this danger inherent in tubelet pockets of nonwoven materials, tubelet pockets made of woven fabrics have become known. The disadvantage must, of course, be accepted that such pockets have a poorer filtering action than nonwoven materials, and that the internal resistance of batteries equipped in this manner is comparatively high.